A successful technique for delivering radioactive seeds to the prostate for treatment of cancer therein is known as transperineal seed implantation. In this technique, a plurality of elongated needles, each loaded with a series of radioactive seeds with spacer elements therebetween, are inserted through the perineum area of the patient into the prostate. The needles are accurately positioned in the prostate using ultrasound and a stepper apparatus, in accordance with a preplanned radiation dosimetry pattern. This technique is described in detail in an article entitled "Ultrasound Guided-Transperineal Implantation for the Treatment of Early Stage Prostate Cancer" by Grimm, Blasko and Ragde, in The Atlas of The Urological Clinics of North America, Vol. II, No. 2, October 1994. This technique, when it can be used, has significant advantages over conventional treatments, among them that it can be accomplished on an out-patient basis, with the patient usually resuming normal activity within a few days.
In this technique, however, when the needle is removed from the prostate, the seeds, even with the spacers remaining in place, can migrate to areas within and without the prostate after the needle has been removed. Such seed migration occurs in approximately 11% of the patients so treated. Also, if the needle is removed too fast, the seeds may be drawn in the direction of the needle removal line, due to a vacuum-like effect which occurs when the needle is withdrawn. A change from the intended position of the individual radioactive seeds in the prostate will result in a change of the radiation dosimetry within the prostate, which is undesirable.
U.S. Pat. No. 4,815,449 to Horowitz shows a delivery system involving a needle-like member which comprises a plurality of connected segments made of a rigid material which is absorbable by human tissue. Each of the segments contains therein a radioactive seed; the segments further are physically interconnected in order to form a needle-like (non-deflecting) device for direct insertion in the prostate. Each segment has an integral projection at one end with a complementary recess on the other end for engagement with the projection of an adjacent element. One segment (the frontmost one) will have a tapered portion to facilitate insertion of the article into the prostate.
Such an arrangement, while perhaps tending to maintain the relative position of the seeds after initial insertion of the article, does not, however, lend itself to ease and accuracy of installation and positioning of the seeds. Also, such an article will typically be quite expensive to manufacture, since each unit must be manufactured with the seeds therein, instead of the practitioner simply loading an empty needle with successive seeds and spacers.